Are Odds for Discovery of Life Unfolding Expontentially? Kepler’s Prolific Discoveries of Multiple-Planet Systems

Transit_still1_strip Within just the first four months of data delivered by NASA's Kepler Space Telescope, astronomers have found evidence for more than 1,200 planetary candidates, of which 408 orbit in systems containing two or more planets.

The experts have discovered that the Kepler systems with multiple planets are much flatter than our solar system. For Kepler to see a transit, the planet's orbit must be edge-on to our line of sight. To see multiple transiting planets, they all must be nearly edge-on.


"We didn't anticipate that we would find so many multiple-transit systems. We thought we might see two or three. Instead, we found more than 100," said Smithsonian astronomer David Latham of the Harvard-Smithsonian Center for Astrophysics.

In our solar system, some planet orbits are tilted by up to 7 degrees, meaning that an alien astronomer looking for transits wouldn't be able to detect all eight planets missing  Mercury and Venus. The systems spotted by Kepler are much flatter, with orbits tilted less than 1 degree.

The multiplanet systems spotted by Kepler are dominated by planets smaller than Neptune. They lack Jupiter-sized gas giants with their massive gravity fields that tends to disrupt planetary systems, tilting the orbits of neighboring worlds.

"Jupiters are the 800-pound gorillas stirring things up during the early history of these systems," explained Latham. "Other studies have found plenty of systems with big planets, but they're not flat."

Multiple-planet systems may offer a chance for confirming the densities of small, rocky worlds. The more massive a planet, the easier it is to detect using radial velocity measurements. Earth-sized worlds in Earth-sized orbits aren't massive enough to make a radial velocity signal that's detectable with present technology.

In systems with more than one transiting planet, astronomers have another option: transit timing variations. They can measure how the time between successive transits changes from orbit to orbit due to mutual gravitational interactions between the planets. The size of the effect depends on the planets' masses.

"These planets are pulling and pushing on each other, and we can measure that," said Smithsonian astronomer Matthew Holman. "Dozens of the systems Kepler found show signs of transit timing variations."

As Kepler continues to gather data, it will be able to spot planets with wider orbits, including some in the habitable zones of their stars. Transit timing variations may play a key role in confirming the first rocky planets with the right temperature for water to be liquid on their surfaces.

The Daily Galaxy via cfa.harvard.edu

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